During the past 20 years several experimental solar houses have been constructed in the United States. These experiments have shown not only that solar heating is technically feasible but that the collector system can be constructed with relatively unsophisticated technologies. What has prevented solar heating from being more widely utilized has been the relatively high cost of the collector system and the ready availability of inexpensive liquid and gaseous fuels. With the cost of conventional heating fuels expected to rise sharply in the coming decade, the development of a truly low-cost solar collector system will make it possible to adopt solar heating on a wide scale.